1. Field of the Invention
This invention relates to gas chromatography (GC) equipment, and more particularly concerns (a) a sleeve unit, which comprises an inlet liner and an inlet liner insert positioned therein, for preparing a sample for gas chromatographic analysis, and (b) the inlet liner insert (packing) itself which preferably comprises an arrangement of gold wire.
2. Background of the Prior Art
In gas chromatography (GC), analysis typically is divided into three stages: (1) sample preparation; (2) separation; and (3) detection. Liquid samples to be tested are vaporized in the sample preparation phase, and conventional gas chromatography (GC) employs liners, most commonly made of glass, as a device where vaporization of the liquid sample takes place. Liners are normally subjected to elevated temperatures, e.g., over 200° C., to enhance the rate of vaporization and reduce sample adsorption on the inner surfaces of the liner. It is common to use packing materials in liners to help promote sample vaporization, trap non-volatile residue, such as solid/high molecular weight contaminants which may be present in “dirty” samples, to prevent column contamination, promote sample vapor mixing to obtain homogenous samples, and assist in reaching an ideal sample vapor residence time in the liner prior to the vapor sample formed in the liner being injected into the GC column. Examples of packing material include glass wool, which represents the dominant packing material employed in modern liners, and porous carbon material.
Glass wool packing material has an entangled configuration of glass wool fibers, making it a suitable material to help promote sample vaporization and to trap non-volatile residue which may be present in “dirty” samples. However, the silanol surface of glass wool is prone to substantial adsorption of organic compounds and has been demonstrated to promote chemical breakdown of many analytes. Further, glass wool is a thermal insulator and therefore is not an ideal material for promoting efficient thermal transfer to the liquid sample mixture to be analyzed. In an effort to overcome surface reactivity and adsorption, glass wool is chemically deactivated. However, the process used to chemically deactivate the glass wool is never really complete, and exposed silanol domains on the glass wool remain after the deactivation process. Further, as the glass wool is handled, its fibers tend to break, thereby exposing new active sites. Also, glass wool packing material is difficult to pack into small diameter and medium diameter inlet liners.
Porous carbon materials, such as CarboFrit packing material, have been described as suitable materials for liner packing. However, commercially available examples of CarboFrit packed liners indicate that CarboFrit packing material is very delicate, having an increased risk of particle fine production when handled. Although there may be a marginal improvement in performance using CarboFrit packed liners rather than glass wool packed liners, the marginal improvement may be seen by some as not justifying the increased cost involved in using CarboFrit packed liners rather than glass wool packed liners.
It would be desirable to have an inlet liner insert (e.g., packing) that promotes sample vapor mixing without completely occluding the vapor path through an inlet liner, that has a surface that is inert and causes little or no breakdown or chemical modification of the sample being tested, that does not permanently adsorb components of the sample being analyzed, that promotes quick temperature transfer (e.g., has a high thermal conductivity) to insure efficient volatilization of the liquid sample to be tested, and that has a high surface area to volume ratio.